The invention relates generally to methods of making porous ceramic bodies, such as are suitable for use in exhaust after-treatment applications. More specifically, the invention relates to methods for controlling pore distribution in porous ceramic bodies.
Porous ceramic bodies are used in a variety of applications, such as exhaust gas filtration applications. In exhaust gas filtration applications, the porous ceramic body contains an array of longitudinal channels defined by intersecting porous walls, which may be bare or coated with oxidation catalyst(s). The channels and walls are typically bounded by a circular or oval skin. For particulate filtration, the channels may be divided into inlet and outlet channels, where the inlet channels are plugged at an outlet end of the porous ceramic body, and the outlet channels are plugged at an inlet end of the ceramic body. Exhaust gas enters the ceramic body through the unplugged ends of the inlet channels, passes through the porous walls into the outlet channels, and exits through the unplugged ends of the outlet channels. With each pass of the exhaust gas through the porous ceramic body, the porous walls collect an amount of particulates from the exhaust gas.
The filtration efficiency of the porous ceramic body is directly proportional to the fraction of particulates collected from the exhaust gas. A diesel particulate filter composed of a porous ceramic body ideally combines high filtration efficiency, low coefficient of thermal expansion for thermal durability, narrow pore distribution and large pore size for low backpressure drop, high strength for structural durability, and low cost. In diesel exhaust filtration, cordierite has been the ceramic material of choice because it is a relatively low-cost material and offers a relatively low coefficient of thermal expansion.